A retired Chinese professor who was taken away by authorities during a live television interview with VOA's Mandarin Service nearly two weeks ago, has been allowed to return home under strict security, close friends told VOA on Monday.

Sun Wenguang, 84, told the friends that after he was detained on August 1, he was moved to several locations including Yanzi Mountain Villa at Jinan Military Region, a military-linked hotel and reception center in Jinan, eastern China, his hometown. He was taken to four places, often staying for one or two days under a security watch, friends said.

After speaking with him on Monday, friends said the professor asked them to contact VOA and relay that he was safe and back home. They said that Wenguang told them security guards searched his home and took away all his cellphones, landline telephone, and computer. His social media accounts are blocked, friends said.

VOA attempted to reach Wenguang on Monday but could not make contact. Chinese authorities have refused to comment on the matter.

Wenguang was taken away during a live telephone interview on the VOA Mandarin television show Issues & Opinions as he was criticizing China's foreign aid and diplomatic strategy in Africa. During the interview, Sun told VOA that authorities were breaking into his house in an attempt to prevent him from speaking out against the government.

The professor returned home after more than 150 alumni of China's Shandong University - where he taught for decades - wrote an open letter to authorities, urging the school to ensure his personal safety and freedom.

Wang Shujun, a co-signer of the open letter, told VOA that he was shocked about the incident, which he thought was outrageous, uncivilized and unconstitutional. He noted that the local authorities in Jinan, the capital of Shandong province, severely hurt China's international image by treating the outspoken critic so rudely and recklessly.

"Even President Xi Jinping wouldn't be happy if he learned what happened to the professor," said Wang in a telephone interview with VOA Sunday.

Chinese authorities, including leaders of Shandong University, have kept silent about the incident involving professor Sun despite continuing inquiries from VOA and other international media.

The Trump administration has said it is concerned about the whereabouts of the retired Chinese university professor.

"We condemn China's ongoing abuse of human rights, in particular, the suppression of the fundamental freedoms of expression, association and peaceful assembly, and the unlawful detention of activists, lawyers, journalists and civil-society leaders seeking to defend those freedoms," a State Department spokesperson told VOA.

The official also said the State Department was grateful for the work of VOA reporters and other journalists in China who "have dedicated their lives and taken great risk to pursue this important work."

Sun was answering questions on the VOA show about an open letter he'd written to Chinese President Xi Jinping, criticizing Chinese aid to Africa when there are so many living in poverty in China.

Sun told the host in Washington that police had entered his apartment and demanded he end the interview. Sun blamed Xi for sending the officers to break down his door.

"I am entitled to express my opinion. This is my freedom of speech," were Sun's last words before the line went dead.

Sun is an outspoken, longtime critic of Chinese authorities. He was arrested during the infamous Cultural Revolution of the 1960s and was sentenced to seven years in prison in 1978 for criticizing Mao Zedong, two years after Mao had died.